In case of the automatic door in electric train, its door is closed and opened by the motor. In the process of door closing and opening, the motor controlling circuit estimates the location or the displacement of the door and enables for the door to be closed or opened naturally and exactly by operating the motor with the driving profile to differentiate the output power depending on the estimated location.
In the estimation method for displacement, there are a type to use the encoder, a sensor for detecting the revolution of the motor (hereinafter referred to as ‘encoder type”) and a type to estimate the revolution amount by sensing the electric current and voltage for driving without suing the additional sensor (hereinafter referred to as ‘sensorless type”)
Firstly, in case of a system adapting the encoder type, an encoder which generates a certain pulses, for example 360 pulses on each turn of the motor is installed on the axle of the motor and the door control unit (DCU) calculates the displacement of the door using the motor revolution and ball screw pitch after estimating the revolving of the motor based on the pulses. This encoder type has simple configuration and algorithm and high reliability on the corresponding outcome, but the exchange is necessary due to the destruction by the reason of low durability and it has limit of noise creation from the operation of encoder.
Next, a sensorless type system detects the counter electric motive force (counter EMF) and electric current which are created in motor driving and the motor RPM and displacement of the door are calculated based on such detection. The sensorless type shall equip with the circuits for measuring the electric current and voltage. At the same time, the sensorless type can be realized in lower cost than encoder type, but it requires additional MCU (Micro Controller Unit) to perform high speed arithmetic process as its arithmetic processing is so complicated. In addition, there is a limitation of difference in its performance depending on the price of the electric current sensor. The selection of motor by the strict standard in consideration of the reliability of the motor is required because its performance is influenced by the deviation of the characteristics of each motor. The adaption frequency of the sensorless type is lower than encoder type relatively because its accuracy lags behind.
Many doors are equipped in a rolling stock of the current railway train and the closing and opening of the door are controlled by using either of encoder type and sensorless type. However, there is a big potentiality of failure creation in controlling the door due to the characteristics of many doors.
In case of failure any one of the doors, there is a limit to stop the driving without particular first aids and to return to the base due to the characteristics of the electric train considering the safety of the citizen in priority. For example, when the failure is created from the encoder in the train adapting the encoder type due to the high voltage and noise, the abnormal signal is created because the displacement of the door cannot be recognized due to the failure of the encoder in the DCU of the train. Here, the engineer has difficulty to take additional first aids because the encoder is attached at the rear part of the motor due to the difficulty of disassembly/assembly and exchange. Consequently, the engineer is forced to return to the base as the normal operation is impossible.
As it is explained, there is a permanent possibility to bring forth such severe inconveniences to the citizens in case of failure on the door of the train.
Consequently, it is inevitable to suggest the technology which does not hinder the normal operation for the convenience of the citizens by adapting the dualization technology which can operate the door normally in case of failure in door controlling of the current train.